Chapter 11

Stephen Hawking discusses the search for a unified theory in physics that would fully explain the behavior of waves and particles at the smallest levels of matter in quantum mechanics and the cosmic behavior of the largest levels of matter under the theory of relativity. He notes that the problem of gravity has not yet been resolved in the quest for such a theory, and introduces string theory as a potential solution. String theory proposes that matter is made of strings that have length but no other dimensions, and can exist in different configurations. However, string theories are only consistent if space-time has 10 or 26 dimensions rather than the 4 dimensions that are perceivable and existent to living beings. There are also multiple competing string theories, which may suggest the existence of more fundamental theories that could unify them. Hawking believes that the overlapping of grand unified theories (GUTs) may form a series of maps that, when pieced together, could offer an accurate picture of an as-yet unknown theory that governs all GUTs. The ultimate goal of this search is to understand the purpose of human existence amid the events around us.